Process for increasing the solubility of the potassium content of cement-kiln dust.



UNITED STATES PATENT OFFICE.

RAYMOND J. NESTELL, OF LOS ANGELES, CALIFORNIA, ASSIGNOR TO INTERNATIONAL PRECIPITATION COMPANY, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF PROCESS FOR INCREASING THE SOLUBILITY OF THE POTASSIUM CONTENT OF CEMENT- Patented July 30, 1918.

CALIFORNIA.

KILN DUST.

1,274,310, Specification of Letters Patent.

No Drawing. Application filed January 15, 1917. Serial No. 142,551.

To all whom it may concern Be it known that I, RAYMOND J. NnsTnLL, a citizen of the United States, residing at Los Angeles, in the county of Los Angeles, State of California, have invented a new and useful Process for Increasing the Solubility of the Potassium Content of CementKiln Dust, of which the following is a specification.

This invention relates to the utilization of the dust collected from the flue gas passing from cement kilns, particularly of the coalfired type. Said dust is now being collected in large quantities by the action of electrical precipitators, and it is found to contain, in many cases, a considerable quantity of potash, making it suitable for use as a fertilizer. In some cases, the potassium content of the dust is, to a greater or less extent, in a Water insoluble form and the fertilizer being generally graded and sold according to the proportion of water soluble potash, there is a serious loss to the seller of this fertilizer, for the reason that he does not get credit for all of the potassium content but only for the water soluble portion thereof. My invention is directed mainly to increasing the amount of water soluble potassium com pound in material of this character so that the producer or seller of this material obtains credit for substantially the full amount of available potash contained in the dust.

I have discovered that when cement kiln dust containing more or less water insoluble potash is subjected for a sufiicient time to the action of hot Water, a considerable proportion of the potassium content of the material is converted into a water soluble form and my invention is based on this discovery.

My invention may be carried out as follows:

The cement kiln dust is placed in a suit- ,able receptacle, for example, a tank into which hot water or steam is passed so as to bring the potassium compound in the dust in contact with water at or about bollmg temperature. After several hours of contact of the material to be treated with the hot water in this manner, most of the potassium content of such material is converted to a water soluble form. Treatment for twentyfour hours with boiling water, will in general, be sufficient, it being of course understood that, as is usual in such cases, temperature and time are within reasonable hmits mutually convertible factors; so that a similar result may be secured in longer time and at somewhat lower temperatures, or conversely, in a shorter time and at correspondingly higher temperatures. Any water remaining with the material may then be evaporated in any suitable manner so as to leave the material in suitable condition for sale and use as a fertilizer, or if desired, the water may be drawn off and evaporated down to recover the potassium compound in a more concentrated condition.

As an example of the process, cement kiln dust which contains about 13% K 0, of which only about 60% was in water soluble form (as determined by extraction with cold water for two weeks), was boiled with hot water for one day, over 96% of the potash present being thereby dissolved. A small portion of the potash in the dust is not rendered soluble by this treatment, this portion being apparently that contained in unchanged rock particles carried over with the fumes and flue gases from the kiln. In fact, the potash content of cement kiln dust from coal-fired kilns may, in general, be said to exist in three forms: 1st,-a readily Water soluble form, consisting apparently of potassium sulfate produced by volatilizat-ion of potassium compound in the feldspar and its precipitation in the form of sulfate by reaction with the gases in the kiln. 2nd,a difiicultly soluble form, consisting apparently of potassium compound which has reverted or become reconverted to silicate form by contact with the silicious material in the dust. This portion is particularly prominent where fire coal dust is used for fuel, the potasstituent so that the recess provides for the recovery of substantlally all of the available potash in the material.

In evaporating the solution to dryness, for the recovery of potassium compound therefrom, I, prefer to utilize the heat oi the line or hiln gases from the cement kilns, said gases being passed under or over or through evaporating tanks or pans, or utilized in any other manner in order to evaporate the solu tion by the heat of saiilgases.

What I claim is: t

1. The process of converting to soluble form the potassium compound present in eementkiln dust in diiiicultly soluble form, which consists in subjecting such dust to the action of water at approximately 100" C. for a suiiicient time to eiiect substantial con version of such compound to a form whieh is readily soluble in water.

2. The process oi recovering tronl eoultired cement kiln dust potassium eonipound present [herein in dillieultly soluble tornn uhich consists in subjecting sueh dust to the action of water at a p 'iroximately 100 (l. for a sutiicient time to effect substantial conversion of such compound to a form which is readily soluble in water, removing the resulting solution from the undissolved residue and treating said solution to obtain the potassium compound therein in concentrated form.

3. The process of recovering from coaltired cement kiln dust potassium compound present therein in ditiicultly soluble form, which consists in subjecting such dust to the action of water at approximately lUU (J. for a su'tiieient time to ettect substantial conmrsion oi such compound to a form which is readily soluble in water, removing the resulting solution from the undissolved residue and evaporating said solution to dryness.

l. The process of treating flue dust from eoal lircd cement kilns, to increase the solubility of diiiicultly soluble potassium eompound therein, which consists in subjectinn sueh dust to the action of hot water at a temperature and tor a time sutl'icient to of feet substantial eonrersion oi sueh ditl'ieultly soluble eolnpouud to a eompound which is readily soluble in \\'.lt(.i.

ln testimony wluareof l have hereunto set my hand, at Los Angeles, California this Bthklay of January 1917.

RAYMOND J. NESTELL.

Coptic of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

